1. Field of the Invention
The present invention relates to an exhaust gas cleaning device for an internal combustion engine having a collector for collecting exhaust particulate matters contained in exhaust gas of the engine.
2. Description of Related Art
In recent years, a collector for collecting exhaust particulate matters has been located in an exhaust pipe of a diesel internal combustion engine mounted to a vehicle to reduce exhaust particulate matters contained in discharged gas. The collector has a porous ceramic body with multiple exhaust flow passages. The collector adsorbs and collects the exhaust particulate matters when the exhaust gas passes through porous partition walls defining the exhaust flow passages. If the exhaust particulate matters collected in the collector are deposited in the collector, a pressure loss increases and engine efficiency decreases. Therefore, the collector is regenerated by combusting the exhaust particulate matters in the collector if the deposition amount reaches a predetermined value.
The deposition amount of the exhaust particulate matters is estimated by using the pressure loss as an input based on deposition characteristics correlating the deposition amount of the exhaust particulate matters in the collector with the pressure loss at the collector. The regeneration of the collector is performed if the estimated exhaust particulate matter deposition amount reaches the predetermined value, for example, as described in JP-A-2004-19523.
Pressure loss characteristics change if ash as residue of combustion of fuel or engine oil in the engine is deposited in the collector. Therefore, a certain device performs the regeneration of the collector if the pressure loss at the collector reaches a predetermined value and increases the predetermined value as the ash deposition amount increases, for example, as described in JP-A-2002-242660.
However, in the device described in JP-A-2004-19523, the deposition characteristics correlating the deposition amount of the exhaust particulate matters with the pressure loss do not take the influence of the ash deposition in the collector into consideration. Accordingly, there occurs a problem that the exhaust particulate matter deposition amount cannot be accurately estimated because of confusion between the change in the pressure loss due to the ash deposition and the change in the pressure loss due to the deposition of the exhaust particulate matters.
The device described in JP-A-2002-242660 determines the regeneration timing of the collector on the assumption that the pressure loss increases as the ash deposition amount increases. However, the pressure loss can decrease as the ash deposition amount increases even if the exhaust particulate matter deposition amount is the same, depending on the ash deposition state such as the deposition amount or deposition position of the ash. Therefore, there occurs a problem that the regeneration timing of the collector cannot be determined appropriately.